1. Field of the Invention
The present invention relates to an improved method for combining waste materials to produce valuable products for agricultural, horticultural, sylvicultural or public use.
Specifically, the present invention relates to a delayed exothermic reaction of alkaline materials with waste materials, such as wastewater treatment plant sludge, animal excrement or process wastes, and additionally with carbon dioxide gas or carbon dioxide solids, to thereby convert said waste materials to useful products such as soil conditioners or fertilizer supplements.
More specifically, the present invention relates to reacting alkaline materials, such as calcium oxide, cement kiln dust, lime kiln dust or similar alkaline materials and combinations thereof with wastewater sludge or animal excrement as well as carbon dioxide gas or carbon dioxide solids in a reactor so as to provide a well blended mixture that reacts exothermically after discharge from the reactor, providing temperatures exceeding the boiling point of water, instantly drying said mixture through rapid evaporation of liquids, dramatically changing the appearance of the product so that the products meet or exceed regulatory requirements for beneficial use of waste materials while improving environmental quality and protecting human health.
2. Description of the Prior Art
Those skilled in sludge management practices are aware that methods for alkaline stabilization or decontamination of waste sludge are presently in use.
In his book titled "Treatment and Disposal of Wastewater Sludges", Ann Arbor Science Inc., publishers, 1979 Edition, P. Aarne Vesilind, reviews the practice of mixing lime and sludge in a common concrete mixer to yield a product which is marketable as a soil conditioner. The sludge is dried and disinfected as a result of an exothermic reaction which approaches (but does not exceed) 100.degree. C.
U.S. Pat. No. 4,226,712 dated Oct. 7, 1980 by Kamei discloses a method of treating water containing wastes by first mixing the waste with an alkaline earth metal oxide such as calcium oxide as a preliminary drying step followed by a second step of removing additional water by drying means at temperatures from 800.degree. C. to 1,450.degree. C. During the first step, the organic sludge is "partly gelated". Kamei also teaches that "the mixture thus heated by the exothermic reaction to a temperature from about 80.degree. C. to 90.degree. C." Additionally, Kamei teaches that the high temperatures do not decompose the organic constituents contained in organic waste and remain in the final product. The sterilized products are used as fertilizers.
In U.S. Pat. No. 4,270,279 dated Jun. 2, 1981, Roediger teaches a method for alkaline stabilization of dewatered sludge cake which results in the formation of sterilized pellets. The claim is that an inexpensive method is provided for sterilizing dewatered sludge cake which is discharged from belt presses wherein the sludge cake is broken into ball-like particles having diameters ranging from 1 to 10 millimeters, dusting these particles with quicklime (calcium oxide) and achieving temperatures "of the bulk matter to about 70.degree. C. to 80.degree. C." The quicklime reacts exothermically with the surfaces of said ball-like particles resulting in a product which can be used as an agricultural product. To achieve complete sterilization, the treated waste had to be stored for four hours. The means for mixing and reacting the sludge with quicklime includes a paddle blender or pug mill.
The RDP Company, Plymouth Meeting, Pa. advertises a so-called "Envessel Pasteurization" process. The process description is that of a screw conveyor or pug mill type mixer that enables reacting dewatered sludge cake and quicklime exothermically, discharging into a jacketed holding hopper, with "supplemental heat added to the vessel to insure the mixture maintains a temperature of 158.degree. F./70.degree. C. for a period of 30 minutes". This process produces a product meeting regulatory agency requirements for PFRP, Process to Further Reduce Pathogens.
U.S. Pat. No. 4,554,002 dated Nov. 19, 1985, granted to Nicholson, discloses a method for beneficiating "low percentage solids" waste water treatment sludge, without prior dewatering, by mixing kiln dust containing a percentage of calcium oxide to form a solidified, disintegratable, friable product which can be eventually granulated after curing and aging for a sufficient period of time. A product is produced which can be applied to land as well as used as a soil conditioner and fertilizer supplement.
Nicholson also disclosed improved methods for treating wastewater sludge in U.S. Pat. Nos. 4,781,842 and 4,902,431. The method "decontaminates" wastewater sludge to a level that meets or exceeds U.S. EPA Process to Further Reduce Pathogens standards. The method mixes sludge with alkaline materials sufficient to raise the pH of the mixture to 12 and above for at least one day, and then the mixture is dried to produce a granular material. So-called "decontamination" is the process of exothermically reacting alkaline materials with sludge to raise the temperature to about 50.degree. C., but not to temperatures sufficient to cause sterilization, thereby reducing and/or eliminating pathogenic microorganisms, but maintaining beneficial non-pathogenic microorganisms, and coupling this step with drying, such as windrowing, to produce a PFRP product.
In U.S. Pat. No. 4,306,978 dated Dec. 22, 1981, entitled "Method for Lime Stabilization of Wastewater Treatment Plant Sludges", granted to the applicant, the subject matter of which is incorporated herein by reference thereto, a method for lime stabilization of wastewater treatment plant sludge is disclosed. The method includes the steps of dewatering sludge and rapidly and intimately mixing and reacting sludge cake with quicklime (calcium oxide) so as to produce stabilized sludge pellets.
In U.S. patent application Ser. No. 546,426 for "Improved High Rate Method for Alkaline Stabilization, Beneficiating and Pelletizing of Wastewater Treatment Plant Sludges now U.S. Pat. No. 4,997,572," also by the applicant, an improved method is disclosed which exothermically reacts alkaline materials with waste material, beneficiates said materials, and forms pellets having a skin of calcium carbonate. The carbonates are formed as the last step of the process by reaction of calcium hydroxide, contained in the pellet, with carbon dioxide gas or carbon dioxide solids (dry ice).
The aforesaid patented methods of the applicant are advantageously and efficiently accomplished in a blender-dryer-reactor invented by the applicant and described in U.S. Pat. No. 3,941,357. The method of U.S. Pat. No. 4,306,978 and the applicants patented apparatus have been widely accepted by the pollution control industry with many successful installations in the United States.
Many of the aforesaid methods of alkaline stabilization or decontamination are presently in practice today, but all have limitations when compared to the new method of the applicant. Because of the increasing demand for viable alternative for disposing of waste materials and the promotion of practices that provide for beneficial use of sludge, the new inventive method addresses the limitations of present methods and provides a beneficial product from waste materials that not only will have appeal for public use by virtue of its physical appearance, but more importantly, because of the high rate, subsequent instant drying with high efficiency, can be shipped long distances without fear of degradation so that said products can be economically used as fertilizer supplements in third world countries.
When compared to the instant invention, none of the aforesaid methods teach the method of obtaining of temperatures in excess of 100.degree. C., such as temperatures up to or exceeding 117.degree. C., which result from the exothermic reactions. Neither do any of the methods delay or retard the exothermic reaction so that the chemical reactions can take place with high efficiency after a highly accurate blending of the components of the mixtures is assured. Those skilled in the art of mixing, blending and reacting materials recognize that materials cannot be commingled or dispersed accurately as said materials are changing stage or state. Another limitation of present inventions is the relatively long drying periods when dried by natural means such as air drying, or the additional equipment and fuel required for drying in a drying apparatus. This compares to the subsequent relatively instant drying as the exothermic reaction takes place at high temperatures exceeding 100.degree. C. for the new method.
Extended drying periods also require costly land storage area as well as additional labor and material handling to transport material to and from said storage area.
Most of the products provided by the methods presently in use have moisture content ranging from 10% to 35%. The products having the least amount of moisture require drying periods of at least 30 days. This is another limitation of the present methods in that the new process can selectively provide a moisture content in the product, ranging from 50% to less than 10%, by varying the ratios of components of the mixture and reaction. Additionally, the new product is so well blended, reacted and dried, that there remains no pockets of unblended material and therefore no pockets containing a higher moisture content which could cause spoilage or degradation over periods of time. The uniform drying of the new inventive product enables its packaging and shipping over long distances without degradation.
The color of products produced by presently existing methods range from black to light gray, whereas the new product has an off-white appearance. This off-white appearance is more acceptable to the public since it does not resemble a product made from waste sludge.
It is accordingly an object of the present invention to provide a novel, improved method for reacting alkaline materials, carbon dioxide and waste materials, such as wastewater sludge, animal excrement or process wastes in a conventional blender-reactor, preferably a plow blender type so as to provide a delayed exothermic reaction after discharge from the blender-reactor, the reaction resulting in the beneficial use of waste materials while improving environmental quality and protecting human health.
It is a further objection of the invention to provide a method of treating sludge wherein temperatures exceeding the boiling point of water are obtained with subsequent relatively instant drying through rapid evaporation of liquids from waste materials while dramatically altering the appearance of the waste products.
It is also an object of the present invention to provide sterile products by thermal destruction of microorganisms, high dry solids content of the product, or a combination of thermal destruction and high dry solids content which is not life supporting.
Accordingly, the invention provides for the reduction in pathogens that is equivalent to and exceeds the reduction of other approved USEPA standards for PFRP, the Process to Further Reduce Pathogens, as per USEPA Appendix II of 40 CFR 257, which standards state in part as follows:
Heat drying: Dewatered sludge cake is dried by direct or indirect contact with hot gases, and moisture content is reduced to 10% or lower. Sludge particles reach temperatures well in excess of 80.degree. C.
Other methods: Other methods of operating conditions may be acceptable if pathogen and vector attraction of the waste (volatile solids) are reduced to an extent equivalent to the reduction achieved by any of the above (other) methods.
In a 1985 memorandum regarding 40 CFR 257 regulations, the USEPA outlined another qualifying PFRP process, namely, the reduction of pathogenic bacteria, animal viruses, and parasites below detectable limits of one plaque forming unit (PFU) per 100 ml of sludge for animal viruses; three colony forming units (CFU) per 100 ml of sludge for pathogenic bacteria; and one viable egg per 100 ml of sludge for parasites. Additionally, vectors such as flies or rats should not be attracted to the product. Since Nicholson per U.S. Pat. Nos. 4,781,842 and 4,902,431 meets the aforementioned standard by providing temperatures of 50.degree. C. and dryness of 65%, the new inventive process exceeds the temperatures of 50.degree. C. with temperatures exceeding 100.degree. C., and with a dryness exceeding 90%.
The present invention also beneficiates waste materials by synergistically combining waste materials such as waste sludge and kiln dusts to thereby effect soil conditioners and fertilizer supplements, the products containing nitrogen, phosphorus, potassium, trace nutrients and organic matter, as well as calcium from calcium carbonate, that can be land applied. The calcium carbonate of the product is known to degrade more slowly than hydrated lime and therefore provides beneficial slow release of alkalinity to cropland. The invention also eliminates the necessity for product storage or extra material handling. It provides a free flowing product that can be marketed as a free flowing powder or as granules, micro-pellets or pellets; have a innoxious odor; reduce vector attraction; reduce bulk density and color so that the products do not appear "sludge-like" to the general public.
The invention also converts and beneficiates waste materials into valuable products for utilization as soil conditioners or fertilizer supplements in agricultural applications for food and feed crops; for horticultural applications such as plants and use in nurseries; for sylviculture to increase forest productivity and revegetate forest lands devastated by fire, land slides, volcanos or other natural disasters; public use such as turf maintenance or production, strip mine reclamation, covering expired landfills; fertilizing highway median strips; or additionally addressing process waste for preparing process waste for approved landfill applications.